Try page 417 in this catalog:
They have two that are for BT35 with M12 threads. The first one, P/N 7-081-B35102, has the 7mm and 10mm dimensions you need and the price is $15.95
If that doesn't work out, I would email the sellers on Ebay who sell the more common CAT40 and BT40 knobs. I suspect they could beat the price or delivery or maybe both, considering they sell regulanobs for nearly half of the catalogs. Maybe they have some or have made them before.